Method of manufacturing pickup tubes



P 24, 1957 F. D. MARSCHKA ETA]. 2,807,517

I I METHOD OF MANUFACTURING PICKUP TUBES Filed Feb. 18, 1955 I INVENTQRS FAHNK 0. MGKSC'fi/Kl,

rramvzr W Auznwsk/ 2,807,51 7 Patented Sept. 24, 1957 2,807,517. METHOD OF MANUFACTURING PICKUP TUBES Frank D. Marschka, Mount Joy, and Franz S. Veith and Henry W. Kuzminski, Lancaster, Pa., assignors to Radio Corporation of America, a corporation of Delaware Application February 18, 1955, Serial No. 489,252 9 Claims. (Cl. 316-25) This invention relates to pickup, or camera, tubes and particularly to a method of, and means for, manufacturing pickup'tubes of the type including a photoconductive target.

In the art of manufacturing pickup tubes it is desirable to evaporate the photoconductive material to produce the target at one end of the tube envelope prior to the sealing of the electron gun into the other end of the tube, as well as prior to the outgassing of the tube proper, and prior to the outgassing and activation of the electron gun. One of the reasons that it is desirable to lay down the photoconductive layer at this time is that, by

United States Patent O fifice so doing, the side tip-off of the side exhaust tube on the envelope, through which evaporation of the photoconductive layer is normally performed, may be eliminated. When the side tip-off is eliminated the tube may be placed more accurately in relation to its associated deflection components in the camera resulting in more uni form magnetic field configurations at the photoconductive surface. In tubes having a side tip-0E these results can be achieved only by using larger diameter and longer magnetic deflection components at the expense of more deflection power and a larger, bulkier camera.

Furthermore, it is desirable to evaporate the photoconductive layer .ata time prior to the stages of manufacturing set forth above so that greater flexibility of evaporation techniques may be obtained resultingin a more uniform photoconductive layer. Still further, it is desirable to evaporate the photoconductive layer at a time prior to the manufacturing stages set forth above so that a higher quality of photoconductive layer may be obtained for, if the evaporation is done at this time, it is not necessary to evaporate the photoconductive layer through the electron beam decelerating mesh screen. Still further, when the evaporation of the photoconductive layer occurs prior to the manufacturing stages set forth above, the methods of manufacture that can be utilized are more economical than previous means for manufacturing tubes of this type.

Although it has been recognized that the above advantages could be accomplished byevaporating the photoconductive target at the stage of the manufacturing process set forth above, ithas not been possible to do this because the pre-evaporated photoconductive layer would have been destroyed, or at best seriously damaged, during the processes of outgassing the tube proper, and outgassing and activating the electron gun. This damage occurs because a temperature greater than 150 C. ruins the semi-conductive properties of the photoconductive material, and at temperatures below this the tube cannot be outgassed sufficiently to operate without a high ion current.

It is therefore an object of this invention to provide a new and improved method of, and means for, manufacturing a pickup tube.

It is another object of this invention to provide a novel method of, and means for, manufacturing a camera tube having a pre-evaporated photoconductive target.

It is a further object of this invention to provide an improved pickup tube.

These and other objects are accomplished in accordance with this invention by providing an improved methodof, and means for, manufacturing a pickup tube. The method includes the steps of: 1) depositing a photoconductive layer on a transparent conductive coating which is supported on a glass support plate, which is mounted in one end of an envelope; (2) mounting a gun assembly including an exhaust tubulation within the other end of the envelope; (3) baking the envelope at temperature less than that which would harm the photoconductive layer, or at greater temperatures while maintaining the photoconductive layer below the critical temperature; (4) degassing the electrodes; and (5) flashing the getters. All of the steps are performed while the temperature of the photoconductive layer is maintained below any harmful temperature. A photoconductive tar- 3 get, and therefore the tube, manufactured in accordance with this invention has a negligible gas ratio, long life, good sensitivity and a useable lag characteristic.

The novel features which are believed to be characteristic of this invention are set forth in the appended claims. The invention itself will best be understood by referring to the following specification when read in connection with the accompanying single sheet of drawings wherein.

Figures 1 through 5 are schematic diagrams of various steps in the process of manufacturing a pickup tube in accordance with this invention.

Referring specifically now to Figure 1 there is shown schematically a diagram of one step of the process of manufacturing a pickup tube in accordance with this invention. In the diagram of the process shown, an envelope 10 has a conductive ring 12 sealed to one end thereof. Also sealed to ring 12 is a glass face plate 14.

positing a photoconductive layer, the envelope 10 is baked in a furnace 28 at a temperature of approximately 300 C. for a period of time of approximately one-half hour. This temperature may be measured by means of a ther mocouple (not shown) against the envelope 10. Dur ing the baking the envelope 10 is supported in furnace 28 so thatseal 24 is approximately one-half inch outside the furnace 28. The seal is kept cool during this time by means such as a blast of air from a source 27.

After the envelope 10 has been processed as described above it is cooled to substantially room temperature and filled with an inert atmosphere, such as argon, ata pressure of approximately 1 mm. of mercury. When this is done photoconductive material in evaporator 18 is evaporated onto the transparent conductive coating 16 by heating the evaporator 18 to a temperature of approxi mately 500 to 600 C. in the inert atmosphere as described above. The presence of the inert atmosphere results in a porous form of photoconductive material having a'high order of sensitivity. When the photocon ductive material has been evaporated, the pressure ofthe evaporator 18-, as well as the-evaporator shield 22, are removed from the envelope. At this time the envelope 10, including the evaporated photoconductive layer, is transferred to an adjacent exhaust system on which a complete gun assembly has .been previously mounted and to which it has been sealed air tight.

Referring now to Figure 2 for additionalprocedures in. accordance with this invention that are performed after the photoconductive layer has been deposited, there is shown schematically the next step in the processing of theenvelopelO. In thisstep the envelope is aligned with a stem 29 whichsupports a gun assembly 30 by means of lead-ins 39. Asis welleknown the gun assembly, or mount SOincludes the usual cathode'31,control-electrode34, accelerating electrode 32 and focusing electrodedii.- At thetarget end of -focussing electrode 33 there is mounted a fine mesh screen 37. During this step-ofthe process the complete-gun assembly 30Jis inserted into the bulb-10, andiis held therein by a conventional means such as bulb spacers (not-shown). The complete gun mountassembly 30 is supported on lead-in "wires 39- which have been pre-sealed to the stom which may be pressed glass.-

Thelead-inwires 39 are forenergizing the various-elec-.

trodes. Thestem includesta n exhaust tubulation 35. The

gun mount; i. e. one having lead-ins 39 and exhausttubw.

lation sealed tostem 29, is carefully aligned-with the' envelope-10w prevent unnecessary strain on :the'stem 29.-

Inserted between the open end of the envelope 10' and the open end of stem 29 is asealing ring 36 which may be .any of'the well known ironchromium alloys. When the stem 29, the sealing ring 36, and the open end-of the en elope 10 are inalignment-and abutting each other, the openend ofthe envelope 10 and the stem 29 are preheated with a soft gas-air flame to a temperature of approximately 400 C. When the presheating step has been accomplished an R. coil-38 is positioned concentric with the sealing ring 36 to make the seal as is wellknown. The approximate temperature required to provide the vacuum tight-seal varies for different glass com positions. For the conventional glass compositions a temperature of approximately 708 C. may be used. When theseal has-been made the sealing area is annealed with a gas-air flame. During the pre-heating, sealing and annealing processes the face plate and photoconductive targetsh ould remain at a temperature, e. g. approximately 125 CL, to-prevent water vapor absorption in the photw conductivelayer. This temperature may be controlled-by utilizing an infrared source 40 adjacent to the. face plate 14.

Referring now to Figure 3 there is-shown schematically the-next step in the manufacture of a pick-up tube in ac cordance with thisinvention. In this step of the process the envelope 10 and its contents are placed in an oven 42 and baked at a temperature of 100 to130 C. for a period of time of approximatel-y one-half hour for the purpose of eliminating any vapor in the envelope. This temperatrim may be measured by a thermocouple (not shown) on the face plate 14. It should be noted that the entire envelope 10 may be inserted in furnace 42-since the temperature of thisfurnace is not sufiicient to harm the photoconductive surface. M

Referring now to Figure 4 there isshown schematically the next step in the process of manufacturing a pick-up tube in accordance with this invention. In this step of theprocess the final bake out of the tube 10 is accomplished in a furnace 44 at a temperature of approximately 400 C. forja period of time of approximately one-half.

hour. It should be noted that in this step of the process the faceplate 14.,is positioned approximately 1 inch ;out-. side the furnace .44 to prevent destroying the photoconductive surface 17.

Referring now to Figure there is shown schematically a representation of the final step in the process. of manufacturing a tube in accordance with this invention. In this step, of the process the envelope is allowed to cool to approximately room temperature. When the envelope 10 is approximately at room temperature-the gun mount and the necessary getters are degassed by means of a RF coil 48, and the cathode activated. At this time the exhaust tubulation 35 is sealed off and the getters are flashed.

In each of the steps shown in Figures 2 through 5 the exhaust tubulation 35 is connected to a pump (not shown) to provide a reduced atmosphere within the envelope 14!. The purpose of the reduced atmosphere is to prevent oxidation of the various parts and .to provide a vacuum adequate for operation of the finished tube. A reduced atmosphere of approximately 10- mm. of mercury is suflicient for this purpose.

What is claimed is:

l. The method of manufacturing a pickup tube comprising the steps of, evaporating a layer of photoconductive material on a signal electrode in one end of an envelope, permanently sealing- .a stem including a premounted electron gun onto the other end of saidenvelope with said electron gun extending into said envelope and annealing said seal while simultaneously maintaining said photoconductor at a temperature below the temperature that would harm said photoconduc-tor, exhausting said envelope, and baking said envelope and its contents while simultaneously maintaining the temperature of said photoconductor below said temperature that would-harm said photoconductor.

2. The method of manufacturing a pick-up tube comprising the steps of, supporting an evaporator shield withing an envelope having one end open, temporarily seal ing said open end to an exhaust system, exhausting said envelope, baking said envelope at a temperature at substantially 300 C., cooling said envelope to substantially room temperature, filling said envelope with an inert gas ate-pressure of approximately 10- mm. of mercury, evaporating a layer of photoconductive material within the other end of said envelope, breaking said temporary seal, removing said envelope from said exhaust system, removing said evaporator shield, permanently sealing a stemhaving a pre-mounted electron gun onto said open end of said envelope with said electron gun extending into said envelope, annealing said permanent seal, maintaining said target at a temperature of substantially 125 C. during said permanent sealing and annealing operations, exhausting said'envelope, baking said envelope and its contents-at a temperature of substantially C., baking said envelope at a temperature, of approxomately 400 C., said'baking operation being done with said target outsideof the furnace at least of an inch, allowing the tubeto cool to approximately room temperature, degassing eleetrodes in said tube and activating the cathode in said electrode gun.

3. The method of manufacturing a pickup tube comprising the steps of evaporating a layer of photoconductive material onto a signal electrode in an envelope, sealing an electron gun into said envelope with said electron gun-extending into said envelope, annealing said seal and simultaneously maintaining said target within a predetermined temperature range during said sealing and annealing operations, exhausting said envelope, baking said envelope and its contents at a temperature of substantially 115 C. fora period of time of approximately one half hour, baking said envelope at a temperature of approximately 400 C. for a period of time of approximately one-half hour, while maintaining said target within said predetermined temperature range during said baking operations, allowing said tube to cool to approximately room temperature, degassing the electrodes within said tube, activating the cathode in said tube, and flashing getter material in said tube.

4. Method of manufacturing a pickup tube having an envelope, said method comprisingthe steps in the order recited of, depositing a photoconductive surface onto a means of evaporating a photoconductive material, sealing a gun assembly on the other end of said envelope, annealing said seal, baking said envelope at an elevated temperature while maintaining the temperature of said photoconductive surface below said elevated temperature and at which said surface is not damaged by said baking, and activating the cathode of said gun assembly.

5. Method of manufacturing a pickup tube having an envelope, said method comprising the steps in the order recited of, filling said envelope with an inert atmosphere at a pressure of substantially l millimeter of mercury, depositing a photoconductive surface within one end of said envelope by means of evaporating a photoconductive material, mounting a gun assembly including an exhaust tubulation on the other end of said envelope, sealing said gun assembly to said other end of said envelope, annealing said seal, maintaining the deposited photoconductive surface at a temperature of substantially 125 C. during said sealing and annealing steps, baking said envelope at a temperature of approximately 400 C. while maintaining the temperature of said photoconductive surface below a predetermined temperature whereby said surface is not damaged by said baking, activating the cathode of said gun, and flashing a getter material in said tube.

6. Method of manufacturing a pickup tube having an envelope, said method comprising the steps in the order recited of, baking said envelope, filling said envelope with an inert atmosphere, depositing a photoconductive surface within one end of said envelope, mounting a gun assembly including an exhaust tubulation on the other end of said envelope, preheating said other end of said envelope, sealing said gun assembly to said other end of said envelope, annealing said seal, baking said envelope, maintaining the deposited photoconductive surface below a predetermined temperature during said sealing, annealing and baking steps, activating the cathode of said gun assembly, and flashing getter material within said tube.

7. Method of manufacturing a pickup tube having an envelope comprising the steps in the order recited of, placing an evaporator assembly including a photoconductive material within said envelope, providing a temporary exhaust stem seal on one end of said envelope, exhausting and baking said envelope, maintaining said temporary seal at a low temperature during said baking step, filling said envelope with an inert atmosphere, depositing a photoconductive surface within the other end of said envelope by evaporating said photoconductive material, removing said evaporator assembly from said envelope, mounting a gun assembly including an exhaust tubulation on the other end of said envelope, sealing said gun assembly to said other end of said envelope, annealing said seal, maintaining the deposited photoconductive surface at a temperature of substantially 125 C. during said sealing and annealing steps, baking said envelope for a period of time of approximately one-half hour at a temperature within the range of 100 C. to 130 C., baking said envelope at a temperature of substantially 400 C. for a period of time of approximately one-half hour, maintaining said photoconductive surface below a predetermined temperature during said baking steps, activating the cathode of said gun assembly, and flashing getter material within said tube.

8. Method of manufacturing a pickup tube having an envelope comprising the steps in the order recited of, placing an evaporator assembly including a photoconductive material within said envelope, providing a temporary seal to one end of said envelope, exhausting said envelope,

baking said envelope at a temperature of substantially 300 C. for a period of time of approximately one half hour, maintaining said temporary seal at a low temperature during said baking step, cooling said envelope, filling said envelope with an inert atmosphere at a pressure of substantially 1 millimeter of mercury, depositing a photoconductive surface within one end of said envelope by means of evaporating said photoconductive material, increasing the pressure within said envelope to break said temporary seal, removing said evaporator assembly from said envelope, mounting a gun assembly including an exhaust tubulation on the other end of said envelope, preheating the area whereat said gun assembly is to be sealed to said envelope to a temperature of approximately 400 C., sealing said gun assembly to said other end of said envelope by heating said seal to a temperature of approximately 700 C., annealing said seal, maintaining the deposited photoconductive surface at a temperature of substantially 125 C. during said sealing and annealing steps, baking said envelope for a period of time of approximately one half hour at a temperature Within the rangeof C. to 130 C., baking said envelope at a temperature of 400 C. for a period of time of one half hour with said photoconductive surface extending out of the baking furnace whereby said surface is not damaged by the temperature within said furnace, cooling said device to substantially room temperature, activating the cathode of said gun assembly, and flashing getter material within said tube.

9. The method of manufacturing a pickup tube comprising the steps of, supporting an evaporator shield within an envelope having one end open, temporarily sealing said open end to an exhaust system, exhausting said envelope, baking said envelope at a temperature at substantially 300 C. for a period of time of approximately onehalf hour, cooling said envelope to room temperature, filling said envelope with an inert gas at approximately 1 mm. of mercury, evaporating a layer of photoconductive material on a transparent conductive'layer in the other end of said envelope, introducing an inert gas into said envelope at a pressure suflicient to break said temporary seal, removing said envelope from said exhaust system, removing said evaporator shield, permanently sealing a stem having a premounted electron gun on said open end of said envelope with said electron gun extending into said envelope, annealing said permanent seal, maintaining said layer of photoconductive material at a temperature of substantially 125 C. during said permanent sealing and annealing operations, exhausting said envelope, baking said envelope and its contents at a temperature of substantially C. for a period of time of approximately one-half hour, baking said envelope at a temperature of approximtaely 400 C. for a period of time of approximately one-half hour, maintaining said layer of photoconductive material within the temperature range of C. to C. during said baking operations, said baking operation being done with said target outside of the furnace approximately 'K; of an inch, allowing the tube to cool to approximately room temperature, degassing the electrodes in said tube, activating the cathode in said electron gun, tipping off said tube, and flashing getter material in said tube.

References Cited in the file of this patent UNITED STATES PATENTS 

